Many hydrocarbon wells are produced by electrical submersible well pump assemblies (ESP). A typical ESP includes a centrifugal pump having a large number of stages, each stage having an impeller and a diffuser. An electrical motor couples to the pump for rotating the impellers. A pressure equalizer or seal section connects to the motor to reduce a pressure deferential between lubricant in the motor and the hydrostatic pressure of the well fluid. Usually, the ESP is suspended on a string of tubing within the well. When operating, the pump discharges well fluid up the string of tubing.
The Well fluid is often a mixture of water, oil and gas. Centrifugal pumps do not operate well when die well fluid produces a large percentage of gas. Sometimes a centrifugal pump can become gas locked and cease to pump well fluid even though the impellers continue to rotate. A gas separator may be employed upstream of the pump to separate at least some gas from the well fluid prior to reaching the pump. The gas separator diverts a portion of separated gas to the annulus surrounding the tubing. The separated gas flows up the annulus and is collected at use well site.
Occasions arise when well fluid flows back down the string of tubing, through the pump and out the pump intake into the well. The well site may lose electrical power to drive the motor, causing this occurrence. An operator may shut down the pump for various reasons, also causing this occurrence. Further, some controllers for ESPs have a feature to break gas locked pumps by rotating the motor and pump in a pumping direction, but at a much slower speed. The slower speed allows well fluid in the tubing to flow downward through the pump in an effort to get the gas within the pump to flow out the pump intake to the tubing annulus.
The downward flow of well fluid through the pump may result in foaming of the well fluid in the annulus surrounding the pump intake and within the interior of the pump. Sometimes, the foam makes it difficult to get the pump to start pumping upward again. The downward flow of well fluid through the pump may also result in sand sliding back down the tubing into the pump. Sand accumulation in the pump is detrimental.